Actn3 knockout mice displayed reduced force generation, reduced fast fiber diameter, increased aerobic enzyme activity, and enhanced recovery from fatigue, mimicking slow fiber characteristics.
Does Actn3 deficiency alter muscle force generation and metabolic properties in a mouse model?
Actn3 knockout mice exhibit a shift in fast muscle fiber properties towards slow fibers, providing a mechanistic explanation for the association between alpha-actinin-3 deficiency and human athletic performance.
A common nonsense polymorphism (R577X) in the ACTN3 gene results in complete deficiency of the fast skeletal muscle fiber protein alpha-actinin-3 in an estimated one billion humans worldwide. The XX null genotype is under-represented in elite sprint athletes, associated with reduced muscle strength and sprint performance in non-athletes, and is over-represented in endurance athletes, suggesting that alpha-actinin-3 deficiency increases muscle endurance at the cost of power generation. Here we report that muscle from Actn3 knockout mice displays reduced force generation, consistent with results from human association studies. Detailed analysis of knockout mouse muscle reveals reduced fast fiber diameter, increased activity of multiple enzymes in the aerobic metabolic pathway, altered contractile properties, and enhanced recovery from fatigue, suggesting a shift in the properties of fast fibers towards those characteristic of slow fibers. These findings provide the first mechanistic explanation for the reported associations between R577X and human athletic performance and muscle function.
MacArthur et al. (Fri,) conducted a other in alpha-actinin-3 deficiency. Actn3 knockout vs. Wild-type was evaluated on Muscle force generation, fast fiber diameter, aerobic enzyme activity, and recovery from fatigue. Actn3 knockout mice displayed reduced force generation, reduced fast fiber diameter, increased aerobic enzyme activity, and enhanced recovery from fatigue, mimicking slow fiber characteristics.